Ronnie and Reggie Kray ran London's East End underworld through the 1950s and 60s with their gang, the Firm, moving from protection rackets and fraud into the murders of George Cornell and Jack "The Hat" McVitie. This film traces that rise using home movies, Pathe and Movietone newsreels, BBC news footage, and clips from the features "Sparrows Can't Sing" and "The Krays," with director Peter Medak recalling how the twins offered his 1962 shoot their protection. Criminal historian Laurie Taylor sets the twins against the East End's older criminal traditions, while brother Charlie Kray, cousins Joe Lee and Rita Smith, and former Firm member Bill Ackerman describe the family and the gang from inside it. Detective Superintendent Leonard "Nipper" Read lays out the investigation that finally convicted them in 1969, and journalists including John McVicar recall the risks of covering the brothers while they still ran the streets. The film also touches on the odd celebrity that surrounded them, nightclub evenings with Diana Dors and Frank Sinatra, before both men went to prison for life.